As metal lines in a semiconductor device are gradually micronized and multi-layered, there occurs a problem that a conventional process of forming an Aluminum line is unable to sufficiently fill up a via hole below a submicron meter. In order to overcome this problem, the conventional method formed a tungsten plug within the via hole by depositing tungsten over the entire structure after forming the via hole, and then etching the deposited tungsten by a blanket etching process.
FIG. 1 shows a sectional view of a device for explaining a problem occurring in a case that tungsten is not over etched performed so as to reduce an etching loss of tungsten in a via hole in the formation of a tungsten plug according to a conventional method.
A First insulating film 2 is formed on a wafer 1. A plurality of underneath metal lines 3 are formed on the first insulating film 2. A second insulating film 4 is formed on the first insulating film 2 including the plurality of the underneath metal lines 3. Some portions of the second insulating film 4 are etched to expose any one of the surfaces of the underneath metal lines 3, thereby forming a via hole. Titanium(Ti) and Titanium Nitride(TiN) are sequentially deposited to form a barrier metal layer 5 on the second insulating film 4 including the via hole. A tungsten plug 6F is formed within the via hole by depositing tungsten on the barrier metal layer 5 and then etching the deposited tungsten by a blanket etching process. In FIG. 1, during the blanket etching process, tungsten is not over etched so as to obtain a preferred tungsten plug 6F. As a result, though a preferred tungsten plug 6F can be obtained without an etching loss of tungsten in the via hole, there remains a tungsten residue 6A at the groove which is created on the surface of the second insulating film 4 due to the differences of topology. The tungsten residue 6A, which induces a bridge effect to occur between neighboring metal lines, has an adverse effect on reliability of the device. Then, an upper metal line 7 connected to the tungsten plug 6F is formed on the second insulating film 4.
FIG. 2 shows a sectional view of a device for explaining a problem occurring in a case that tungsten is over etched so as to prevent a bridge effect between neighboring metal lines in the formation of a tungsten plug according to a conventional method.
The process before the barrier metal layer 5 is formed, is same with the process explained in FIG. 1. A tungsten plug 6F is formed within a via hole through a tungsten lamination process and a blanket etching process. However, in order to solve the problem occurring due to the tungsten residue 6A as shown in FIG. 1, as an over etching is performed in the process of the blanket etching process, the upper portion of the tungsten plug 6F is heavily conceived and thus it reduces reliability of the device because of misconnection with the upper metal line 7 which is formed thereafter. In addition, as the barrier metal layer 5 is damaged as indicated 5A and thus it weakens an adhesive strength between the second insulating film 4 and the upper metal line 7, there occurs a problem that reduces reliability of the device due to a lift effect of the upper metal line 7.